CII Compliance and Vessel Performance Monitoring in 2026

The Carbon Intensity Indicator (CII) framework has entered its operational enforcement phase, requiring continuous vessel performance monitoring and annual verified reporting. IMB Class outlines best practices for data collection, rating calculation, and corrective action planning for 2026 and beyond.

Understanding the CII Rating Framework

CII measures a vessel's annual carbon intensity, calculated using total fuel consumption data and transport work expressed as DWT × nautical miles (for cargo ships) or GT × nautical miles (for passenger vessels). Ships are rated A through E annually: A and B indicate superior and above-average performance; C is the required minimum; D and E indicate below-average and inferior performance respectively.

The required annual CII value tightens by 2% per year through 2030, meaning a ship maintaining the same absolute fuel efficiency will drift toward lower ratings over time. This makes proactive performance improvement essential, not optional.

Fuel Oil Consumption Data Collection

Accurate fuel consumption data is the single most important factor in CII compliance. Data errors — whether from inconsistent bunkering records, flow meter calibration drift, or voyage data attribution errors — can result in artificially high or low CII values that mislead operators and create audit vulnerabilities.

SEEMP Part III Obligations

SEEMP Part III is the primary compliance document for CII obligations. It must describe the ship-specific data collection methodology, record the annual attained CII, and set operational CII targets for improvement. SEEMP Part III must be verified by an approved verifier — such as IMB Class — annually before 31 December.

Ships receiving a D rating for three consecutive years, or an E rating for any single year, must submit a corrective action plan approved by the flag administration within 30 days of receiving the annual rating. IMB Class supports operators in developing and submitting compliant corrective action plans.

Operational Measures for CII Improvement

Speed optimization is the single most impactful operational measure, as fuel consumption scales approximately with the cube of speed. A 10% reduction in speed typically yields a 27% reduction in fuel consumption per nautical mile. Trim optimization, weather routing, propeller and hull cleaning schedules, and auxiliary machinery management collectively contribute further reductions.